<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container {
            width: 100%;
            height: 100vh;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        .box {
            width: 200px;
            height: 100px;
            color: #fff;
            text-align: center;
            font-size: 18px;
        }
        .flex {
            background-color: #f44336;
            display: flex;
            justify-content: center;
            align-items: center;
        }
        .position {
            background-color: #4caf50;
            position: absolute;
            top: 50%;
            left: 50%;
            transform: translate(-50%, -50%);
        }
        .table {
            background-color: #2196f3;
            display: table;
        }
        .table:before {
            content: '';
            display: inline-block;
            height: 100%;
            vertical-align: middle;
        }
        .table .box {
            display: inline-block;
            vertical-align: middle;
        }
        .grid {
            background-color: #9c27b0;
            display: grid;
            place-items: center;
        }
    </style>
</head>

<body>
    <div class="container">
        <div class="box flex">Flexbox</div>
        <!-- <div class="box position">Position & Transform</div> -->
        <!-- <div class="box table">Table</div> -->
        <!-- <div class="box grid">Grid</div> -->
    </div>
</body>

</html>